RE: Shock spacers
Not true.
A lot of people that run threaded shocks use the spacers so they can equally wind the lock rings into place. They then leave them there to prevent the nut from moving as in your pic. The Idea of preloading the spring doesnt increase the rate of the spring (so your thinking is correct there) but to help set the ride height of the chassis. Normally though if your running over 15mm of spacers then your oil wt or qty is wrong.